Electrons are emitted from a conductor when the conductor is:
A. Exposed to weak light
B. cooled rapidly
c.bombarded by high-speed electrons
d.subjected to a small voltage
c. Photomultiplier tube light detectors use this principle.
See
http://quarknet.fnal.gov/projects/pmt/student/dynodes.shtml
for a discussion
The process is called secondary emission.
The answer to this question is option (c) - "bombarded by high-speed electrons."
To understand why, let's break down the options and analyze them one by one:
A. Exposed to weak light: When a conductor is exposed to weak light, electrons in the conductor may absorb energy from the light photons. However, this energy is usually not strong enough to cause the electrons to be emitted from the conductor. So, this option is not correct.
B. Cooled rapidly: Cooling a conductor rapidly can affect its electrical conductivity, but it does not directly result in the emission of electrons. Therefore, this option is not correct either.
C. Bombarded by high-speed electrons: This option is correct. When a conductor is bombarded by high-speed electrons, the collisions between these electrons and the atoms of the conductor can provide enough energy to knock some of the electrons out of the conductor, causing their emission.
D. Subjected to a small voltage: Applying a small voltage to a conductor can generate an electric field, which can influence the movement of electrons. However, it does not directly cause the emission of electrons from the conductor. Therefore, this option is not correct.
In summary, the correct answer is option (c) - "bombarded by high-speed electrons" because it describes a process that can generate enough energy to cause electrons to be emitted from a conductor.